Simulated Effects of Two Fire Regimes on Bighorn Sheep: The San Gabriel Mountains, California, USA

An isolated population of bighorn sheep (Ovis canadensis nelsoni) occupies fire-adapted chaparral ranges in the San Gabriel Mountains, California, USA. During 1976 to 2006, the amount of high-suitability habitat on bighorn sheep winter-spring ranges resulting from fires (HSF) ranged from 670 ha to 3392 ha, and population estimates for sheep, which were correlated with HSF, ranged from 130 to 740 individuals. During the past 100 years, the majority of changes in the HSF were associated with a fire regime dominated by periodic large, wind-driven, high-intensity crown fires, which resulted in high variability in the HSF. Prior to European settlement, the fire regime likely included smaller, variable intensity fires that burned during summer, but that also would have influenced the HSF. The size of those smaller fires today is effectively constrained by current fire management strategies, including exclusion and suppression. We predicted that smaller summer fires would increase the amount of high-suitability habitat and reduce the variability observed in the HSF during contemporary times, and the outcomes of our comparisons were consistent with those predictions. Small fires can be implemented by prescription, and can help to stabilize and maintain a self-sustaining population of bighorn sheep in the San Gabriel Mountains.